1. Field of the Invention
The present invention relates to a process for the preparation of fibre reinforced metal matrix composites and novel preforms therefor.
2. Discussion of the Prior Art
A composite is a material which consists of fibres in a common matrix. The mechanical properties of the composite depend upon many factors which include the orientation of the fibres within the composite body.
Composites may be prepared by interposing layers of fibres between layers of metal and densifying the resulting body. The layer of fibres may comprise a number of aligned continuous fibres. With such arrangements it has been found that where adjacent fibres are touching, or nearly touching, a weakness can occur in the final composite body. It is therefore of great advantage to have a process for preparing a reinforced fibre metal matrix composite where fibre/fibre contact is kept to a minimum.
A known method for the preparation of fibre reinforced metal matrix composites involves aligning the fibres and spraying the fibres with a binder material to prevent the fibres moving during the lay-up procedure. Prior to densification, the binder material must be removed and during this stage fibre movement is known to occur.
Alternatively, the fibres may be held together by weaving with a fine metal wire or ribbon to produce a mat-like structure. The fibres are then placed between layers of metal. This particular method can result in fibre damage and the resulting distribution and volume fraction is often less than desirable.
Also known is a method where the matrix metal is plasma sprayed onto a bed of aligned fibres. This method is disclosed in GB-A-2239262. Problems encountered with this method include matrix contamination, limited availability of suitable matrix materials and the requirement of high capital investment.